UIKitの遅延描画(改)

YMGraphCell.h

#import <UIKit/UIKit.h>

@interface YMGraphCell : UIView

// オーバーライドして、遅延描画
- (void)drawRectAsync:(CGRect)rect andContext:(CGContextRef)context;

@end

YMGraphCell.m

#import "YMGraphCell.h"

@interface YMGraphCell()
{
    UIImage* cache_;
}

- (void)callDrawRectAsync:(CGRect)rect;

@end

@implementation YMGraphCell

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        
    }
    return self;
}

- (void)callDrawRectAsync:(CGRect)rect
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        
        CGFloat scale = [[UIScreen mainScreen] scale];
        
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        CGContextRef context = CGBitmapContextCreate(NULL, scale*defaultSize_.width, scale*defaultSize_.height, 8, scale*4*defaultSize_.width, colorSpace, kCGImageAlphaPremultipliedLast);
        
        CGContextTranslateCTM(context, 0, scale*defaultSize_.height);
        CGContextScaleCTM(context, scale, -scale);
        
        [self drawGraphAsync:rect andContext:context];
        
        CGImageRef image = CGBitmapContextCreateImage(context);
        cache_ = [UIImage imageWithCGImage:image];
        CGImageRelease(image);
        CGColorSpaceRelease(colorSpace);
        CGContextRelease(context);
        
        dispatch_async(dispatch_get_main_queue(), ^{
            self.layer.contents = (id)[cache_ CGImage];
        });
    });
}

- (void)drawRectAsync:(CGRect)rect andContext:(CGContextRef)context
{
    // オーバーライドして遅延描画
}

- (void)drawRect:(CGRect)rect
{
    
    if (!cache_) {
        [self callDrawRectAsync:rect];
        return;
    }
}

@end